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Can I Overfill The Radiator?

02-27-2006, 03:19 PM
I keep having my radiator overflowing and filling up my overflow tank and then spewing coolant out of the overflow hose. I have replaced the water pump, radiator, thermostat, radiator cap, temp. sensor, and various radiator and coolant hoses within the last year or so but still have this problem. I have also "bled" the system by letting the car warm up with the radiator cap off and let the air in the system bubble out. But I have always had the habit of filling the radiator to the "brim" of where the cap mounts and have read that you should fill it only 1/2 to 1 inch below that line because of the expansion of the fluid as it heats. Which of course you can see when you let it heat up without the cap on and it starts to spill over the top of the radiator. So could it be that I am overfilling the radiator and it is causing to boil over or something when it gets hot and increases pressure?

02-27-2006, 03:51 PM
sounds like a blown headgasket to me

02-27-2006, 04:01 PM
Except, no steam (or white smoke) in the exhaust or coolant in the oil. And it's been that way for some time over thousands of miles of commuting driving.

02-28-2006, 11:32 AM
Not knowing what area of the country you are living in, I feel one should ask you what
percent ethylene glycol you are using?

If it is very low percent, close to just water, it WILL boil over........

Maybe just a dumb question, but need to be asked.

I ran just water in an American car (AMC) many years ago on a trip and it constantly boiled
over because water boils too low a temp for modern engines.

I normally run 50% antifreeze for the freeze protection and boilover protection.


03-01-2006, 11:18 PM
carbon buildup inside your engine can also cause pre-detonation. Pre-detonation can, and will cause some hot-spots in your engine, causing even a 100% glycol mix to boil instantly. Once you get a vapor pocket, the pressure in your cooling system will go through the roof, and blow off enough coolant to fill the overflow tank. Try running a couple tanks of 94 octane through it, clean things up a bit.

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